1. Field of the Invention
The present invention relates to a lithium ion secondary battery and a method for manufacturing the lithium ion secondary battery.
2. Description of the Related Art
In recent years, lithium ion secondary batteries have been under development. Because of their high thermal stability, lithium-containing composite oxides having olivine structures, such as LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4, have been expected as positive electrode active materials of lithium ion secondary batteries. Such a lithium-containing composite oxide having an olivine structure contains a bivalent transition metal element (e.g., Fe, Mn, Co, and Ni).
As a method for manufacturing lithium-containing composite oxides having olivine structures, a solid phase method, a hydrothermal method, a sol-gel method, or the like is used (e.g., Patent Document 1). In order to increase the discharge capacity and the energy density of a lithium ion secondary battery, attempts have been made to reduce the particle diameters and variation in particle size of an active material included in an active material layer that relates to insertion and extraction of ions functioning as carriers. A hydrothermal method has been used as a method for manufacturing lithium-containing composite oxides with less variation in particle size and small particle diameters.